Project Summary/Abstract Reactive oxygen species (ROS) cause oxidative stress and play an important role in the pathogenesis of various diseases. However, the exact mechanism of ROS action is unknown. ROS oxidize DNA, proteins, lipids, and small molecules. Carbonylation is one mode of protein oxidation that occurs in response to iron- catalyzed, hydrogen peroxide (H2O2)-dependent oxidation of amino acid side chains. Although carbonylated proteins are generally thought to be eliminated by the proteasome-dependent degradation, my laboratory discovered the protein de-carbonylation mechanism, in which formed carbonyl groups are enzymatically eliminated without proteins being degraded. Major amino acid residues that are susceptible to carbonylation include proline and arginine, both of which get oxidized to become glutamic semialdehyde that contains a carbonyl group. Further, the oxidation of glutamic semialdehyde produces glutamic acid. Thus, I hypothesize that, through the ROS-mediated formation of glutamic semialdehyde, proline, arginine and glutamic acid residues within the protein structure may be interchangeable. Our recent mass spectrometry results demonstrated that proline 45 (a conserved residue within the catalytic sequence) of the peroxiredoxin 6 protein molecule can be converted into glutamic acid in human cells, establishing a revolutionizing concept that iron-catalyzed oxidation elicits the amino acid conversion within the protein structure in the biological system. The objective of this R21 project is to define the occurrence of oxidant- mediated amino acid conversion as a novel mechanism of oxidative stress. The objective of this application will be accomplished by pursuing two specific aims: 1) Identify the occurrence of oxidant-mediated amino acid conversions in cultured human cells and in intact animals; 2) Define functions of oxidant-mediated amino acid conversions. The proposed work is highly innovative because it will address a revolutionizing concept that site-directed mutagenesis/protein engineering-like events occur naturally. Results will be significant because they are expected to provide a new molecular mechanism through which ROS cause biological damage and help develop strategies to prevent and/or treat various diseases.